Influence of radiation therapy on the outcome of T1-2N0M0 triple-negative breast cancer: A SEER population-based retrospective analysis.

e12073 Background: For T1-2N0M0 breast cancer after surgery and axillary staging, the current NCCN guideline recommends radiation therapy (RT) after lumpectomy but not total mastectomy unless there is a positive or less than 1 mm negative margin. This recommendation is regardless of hormonal status. Triple-negative breast cancer is a generally considered more aggressive compared with hormone positive breast cancer. We sought to investigate whether there is a survival benefit of RT in T1-2N0M0 TNBC. Methods: A Population-based retrospective analysis was performed using the Surveillance, Epidemiology, and End Results (SEER) database. Patients included in the analysis were divided into three groups according to surgery modality and RT: breast conservation therapy (BCT, i.e., lumpectomy + RT), mastectomy alone, and mastectomy + RT. The survival endpoints were breast cancer-specific survival (BCSS) and overall survival (OS), and survival analysis was performed using the Kaplan-Meier method. Results: A total of 22473 female with T1-2N0M0 TNBC diagnosed between 2010 and 2015 were included, with 13395 (60%) T1 and 9078 (40%) T2 cases. Surgery, RT and chemotherapy was done in 21674 (96%), 9633 (43%) and 14651 (65%) patients, respectively. Patients who underwent RT were older ( > 50 years, 78% vs 72%, P< 0.001), had fewer T2 (35% vs 44%, P< 0.001) tumor, and had more chemotherapy utilization (72% vs 60%, P< 0.001). 8807 patients had BCT; 8329 had mastectomy alone and 635 had mastectomy + RT. The 5-year BCSS rate was 94.3% for BCT, 93.3% for mastectomy alone ( P= 0.009 vs BCT), and 83.7% for mastectomy + RT ( P< 0.001 vs BCT and P< 0.001 vs mastectomy alone), respectively. The 5-year OS rate was 88.6% for BCT, 83.0 % for mastectomy alone ( P< 0.001 vs BCT), and 79.6% for mastectomy + RT ( P< 0.001 vs BCT and P= 0.190 vs mastectomy alone), respectively. Conclusions: In patients with T1-2N0M0 TNBC, BCT was associated with superior BCSS and OS compared to mastectomy with or without RT. After mastectomy, there was no evidence of survival benefit of RT, with worse BCSS and similar OS.